Processing a flip chip is similar to conventional IC fabrication, with a few additional steps. Near the end of the manufacturing process, the attachment pads 102 of chip 101 are metalized to make them more receptive to solder as shown in FIG. 1A. A small dot of solder such as solder ball 103 is then deposited on each metalized pad such as pad 102 as shown in FIG. 1B. The chips are then cut out of the wafer as normal.
To attach the flip chip 101 into a circuit, the chip 101 is inverted to bring the solder dots down onto connectors (e.g., connector pad 105) on the underlying electronics or circuit board 104 as shown in FIG. 1C. The solder is then re-melted to produce an electrical connection as shown in FIG. 1D. This also leaves a small space between the chip's circuitry and the underlying mounting. In most cases an electrically-insulating adhesive is then “underfilled” to provide a stronger mechanical connection, provide a heat bridge, and to ensure the solder joints are not stressed due to differential heating of the chip and the rest of the system. The underfill distributes the thermal expansion mismatch between the chip and the board, preventing stress concentration in the solder joints which would lead to premature failure.
Flip chip connection is the most popular for commercial integrated circuit package to date; conductive bumps which are connected from bare die side to substrate side for electric signal propagation. The advantage of flip chip interconnection is short signal propagation path, low loss and impedance controllable. However, in millimeter wave frequency range, flip chip interconnection still has certain significant parasitic effect and therefore proper impedance compensation for achieving desire impedance is necessary.